1. Field of the Invention
The invention relates to a sealing element for sealing the transition between the melt channel (which conducts a polymer melt) of a permanently mounted component into the melt channel of a removable, interchangeable component in spinning systems used for spinning polymer melts. Preferably, the permanently mounted component is a spinning beam and the interchangeable component is a nozzle adapter of a melt spinning system.
2. Summary of the Related Art
In spinning systems used for spinning polymer melts, adapters, or nozzle adapters are used to connect the heating container (also known as a spinning beam) and the individual spinning package so that each individual spinning package can be easily removed and replaced for cleaning purposes and for reassembly of the individual parts of the spinning package. Metal O-rings in face grooves are normally used to seal off the spinning channel running from the spinning beam to the adapter, so that spinning operation pressures ranging from a minimum of 80 to a maximum of 350 bar (depending on the polymer) at spinning temperatures ranging from more than 150xc2x0 C. to no more than 320xc2x0 C. do not result in leakage of the polymer melt. If the adapters themselves are replaced frequently, the counter-surfaces must be made of crush-proof materials, e.g., in the form of welded-on stellite cladding, so as to guarantee the seal during longer periods of operation. The O-rings are glued into the face grooves to prevent them from falling out during assembly. Furthermore, these sealing rings, which are expensive, are only intended for single use and must be replaced whenever the adapter is replaced.
The frequency of adapter replacement is especially high during spinning processes that require that the melt be homogenized by a static mixer located as closely as possible to the spinning nozzle. In such cases, this mixer is usually installed in the adapter, as the process requires that it be frequently replaced or routinely cleaned.
The assembly problem associated with the above type of system is that the spinning system must be assembled when it is cold, i.e., at normal room temperature, while replacement of the adapter, with or without a mixer, must take place under hot operating conditions. The component being replaced, in this case the nozzle adapter, is removed while it is hot and is replaced by a cold, fresh component. This procedure applies not only to the aforementioned nozzle adapter, with or without a mixer, but applies more generally to all components that contain lines to conduct polymer melt and that are equipped with any additional parts that require frequent replacement.
A similar situation exists in injection molding technology, in which the thermal expansion coefficient of the construction material is used (e.g., U.S. Pat. No. 5,720,995). In this case, the space between the feed head and the spray head, which space fluctuates in response to temperature, is counterbalanced by a sliding connection piece whose short end is screwed into the feed head and whose long end is displaceably inserted into the bore of the spray head. The fit between the connection piece and the bore and the mating of material (a copper-beryllium alloy for the connection piece and normal steel for the spray head) is selected in such a way that displacement of the long connection piece can take place in the bore to counterbalance the variable space between the feed head and the spray head, even at operating temperatures. Only the narrow and long gap between the connection piece and the bore is used for sealing purposes. Naturally, there must be sufficient space between the long portion of the connection piece and the end of the bore so that the sliding and expansion motion can take place. This space, which represents an expansion of the normal melt channel up to the outside diameter of the connection piece, forms a so-called dead space in which the polymer cannot adequately replace itself. This undefined dwell time, which leads to the breakdown of the polymer, is highly detrimental to the spinning process. The presence of any leaks is also unwanted. Furthermore, assembly and disassembly can only take place when the equipment is in its cold condition, thus shortening usage time by the amount of time it takes the system to cool down.
The foregoing disadvantages of the prior art are addressed by the present invention, which provides a sealing element that allows for frequent component replacement under cost-effective and comfortable conditions, while simultaneously guaranteeing a secure seal.
This is accomplished according to the invention with a sealing element that comprises a cylindrical and externally smooth hollow object with an axial bore for passage of the melt, which object is inserted into a fitting socket hole in an interchangeable component and is made of a material with a higher thermal expansion coefficient than that of the surrounding material of the interchangeable component. The dimensions of the hollow object and the composition and physical characteristics of the material of which it is made are chosen relative to that of the socket hole such that at temperatures distinctly below the polymer melt temperature (preferably at room temperature) the hollow object slides easily into the socket hole, whereas a the polymer melt temperature the hollow object expands against the socket hole to form a tight fit.